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Uncovering friction dynamics using hydrogel particles as soft ball bearings

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Abstract

Rolling ball bearings are widely known and applied to decrease friction between two surfaces. More recently, hydrogel–hydrogel tribopairs have also revealed good but rather complex lubrication properties. Here, we use hydrogels as ball bearings to elucidate that soft spherical particles have nontrivial rate-dependent lubrication behavior. Unlike Newtonian lubrication or dry solid friction, hydrogel particles in suspension transition through four frictional regimes as a function of sliding velocity. We relate the different regimes to the deformation of the particles at different gap sizes, which changes the effective contact area between the sliding surfaces. By systematically varying the particle characteristics and the surface properties of the sliding surfaces, we assign potential mechanisms for each of the different lubricating regimes as a function of velocity: (I) relatively high friction due to particle flattening and direct contact between interacting bodies (II) decrease of friction owing to the presence of rolling particles (III) large inflow of particles in a confined space leading to compressed particles and (IV) the formation of a thick lubricating layer. Using these suspensions with soft, deformable particles as a ball bearing system, we provide new insights into soft material friction with applications in emulsions, powders, pastes or other granular materials.

Graphical abstract: Uncovering friction dynamics using hydrogel particles as soft ball bearings

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Article information


Submitted
13 Jan 2020
Accepted
16 Mar 2020
First published
19 Mar 2020

This article is Open Access

Soft Matter, 2020, Advance Article
Article type
Paper

Uncovering friction dynamics using hydrogel particles as soft ball bearings

R. E. D. Rudge, J. P. M. van de Sande, J. A. Dijksman and E. Scholten, Soft Matter, 2020, Advance Article , DOI: 10.1039/D0SM00080A

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